1. Field of the Invention
The present invention relates to a metal gasket to be installed between the cylinder block and cylinder head of an engine.
2. Description of the Prior Art
It is common practice to install a metal gasket between the cylinder block and cylinder head of an engine to hermetically seal the combustion chamber.
As shown in attached reference FIG. 16, a metal gasket is sandwiched between a cylinder head and a cylinder block of an engine. Movement in the engine, chiefly in the transverse direction, imposes a large lateral stress onto a periphery of a folding part of a stopper so that a crack is often generated thereon. In practice, a. cylinder block is constructed from cast iron and a cylinder head is made from an aluminum alloy. However, the coefficients of thermal expansion of both materials differ significantly. As a result, movement of an annular pressure receiver attached to the cylinder block differs from that of a stopper attached to the cylinder head so that a large stress occurs on the periphery of the folding part during a temperature change of the engine. Particularly if the metal gasket consists of only a first gasket-constituting plate, the abovementioned difference is amplified and the stress acting on the periphery of the folding part is amplified.
The metal gasket for this purpose is usually constructed as follows: It is composed of a beaded plate (which is an elastic metal plate) and a stopper plate placed on top of the other. The beaded plate and stopper plate each has openings at the positions corresponding to the cylinder holes of the engine. The beaded plate has an annular bead (bulging toward the stopper plate) formed in the vicinity of the periphery of the opening. The stopper plate has a stopper (folded back toward the beaded plate) formed in the vicinity of the periphery of the opening. Thus, when the cylinder head is fixed to the cylinder block by means of a plurality of cylinder head tightening bolts, the stopper forms a space equal to its thickness in the vicinity of the bead so as to prevent the bead from being anomalously deformed.
It is also known that the beaded plate and stopper plate are provided with a coating layer of rubber (such as NBR rubber and fluororubber) so as to improve the metal gasket in sealing performance.
The above-mentioned metal gasket poses a problem associated with deformation. That is, the stopper formed on the stopper plate deforms the stopper plate surrounding the stopper convexly toward that side on which the stopper is formed. Likewise, the bead formed on the beaded plate deforms the beaded plate surrounding the bead convexly in the direction in which the bead bulges.
This deformation leads to an uneven rubber coating layer on the stopper plate and beaded plate, and the uneven coating layer results in poor sealing. In addition, the deformed stopper plate and beaded plate do not fit well to each other, resulting in the metal gasket deforming as a whole. Thus the deformed metal gasket is not snugly inserted between the cylinder block and cylinder head.